We are building our derby field this year and I was think about putting in a grob as that would be a great source of dirt for use in our bank complex. My biggest concern is standing water in the bottom. How do course designers keep them dry? I was thinking a French drain would probably be the best option (although most time intensive in building) or do people just pump out the water as needed? Also, do you prefer lining the sides with timbers (or rock/etc) to prevent possible erosion and for asthetics or do you prefer just having grass sides?
Thanks! And by the way, don't google search "how to keep grob dry"... It will assume you are asking how to keep your 'groin' dry!
I won't be able to be of much help, never having built one, but many grobs have a dry ditch at the lowest point, which I would think could help with the drainage aspect if you make it deep enough (a dry ditch is basically a shallow ditch filled with rounded stones).
As for the sides, most horses would probably feel more comfortable with sloped grass sides because it would feel less claustrophobic. I've never heard of erosion issues.